霸县凹陷古近系烃源岩生物标志化合物特征及对油气成藏的贡献

Development characteristics of biomarkers in Paleogene source rocks and its significance to petroleum accumulation in the Baxian Sag

综合利用地球化学、测井、地震等资料研究霸县凹陷烃源岩的生烃潜力、有机质类型、母质来源及沉积保存条件。根据烃源岩与原油的生物标志化合物参数特征进行油源对比,厘清各套烃源岩对油气成藏的贡献。研究结果表明,霸县凹陷发育沙四段、沙三段下亚段及中亚段、沙一段下亚段4套烃源岩,具有生排烃潜力大、有机质类型好的特点,且均已进入生烃门限。其中,沙四段和沙三段下亚段、中亚段烃源岩分布较广,沙一段下亚段烃源岩仅分布于研究区南部地区。生物标志化合物参数分析结果揭示,研究区4套烃源岩的有机质输入与沉积保存条件存在差异,沙四段和沙三段下亚段有机质供应相对于沙三段中亚段和沙一段下亚段充足,但是沉积保存条件却相对较差。通过油源对比发现,霸县凹陷的原油可以分为3类单源油及2类混源油,沙三段下亚段和中亚段烃源岩是现今已发现油藏的主力贡献烃源岩,沙四段烃源岩的有机质丰度较高、生烃潜力大,但已发现以沙四段烃源岩提供油源的油藏多呈近源零星分布于深层及潜山,表明霸县凹陷以沙四段烃源岩为油源的深层及潜山油藏应具有较大的勘探潜力。

Through analyses of TOC,Rock-Eval,biomarker compositions and drill and seismic data,this study was undertaken to investigate the hydrocarbon generation potential,organic matter types,organic matter input and sedimentary and preservation environment of source rocks in the Baxian Sag. Based on source-related biomarker parameters of the source rocks and oil,a detailed oil-source correlation was conducted to identify the origin of oil and to evaluate hydrocarbon contributions of each set of source rocks. The result shows that there are four sets of high-quality source rocks developed respectively in the fourth member of Shahejie Formation(E_2s_4),the lower third member of Shahejie Formation(E_2s_3~L ),the middle third member of Shahejie Formation(E_2s_3~M )and the lower first member of Shahejie Formation(E_3s_1~L ),among which hydrocarbon source rocks in E_2s_4,E_2s_3~L and E_2s_3~M are distributed widely and the source rocks in E_3s_1~L are only distributed in the south-—e—rn— of— th—e —stu—d—ied— a—re—a. And these source rocks are characterized of good type of organic matter and great potential for hy-drocarbon generation and expulsion. The four sets of hydrocarbon source rocks have entered into hydrocarbon generation threshold and are thermally mature. The characteristics of biomarker parameters reveal that the original input and sedimentary preservation environments of organic matter are different. The source rocks in E_2s_4 and E_2s_3~L have more abundant organic matter supply than those in E_2s_3~M and E_3s_1~L ,however,sedimentary preservation conditions at the stages of E_2s_3~M and E_3s_1~L are relatively poor. From the oil-source correlation,three oil families were derived from the source rockes in E_2s_4,E_2s_3~L and E_3s_1~L respectively,and two types of mixed oil were identified. By analysis of hydrocarbon generation potential of the source rocks,their spatial distribution and distribution of their related traps,it is concluded that the main hydrocarbon source rocks for traps that have found are developed in E_2s_3^(M -L). The source rocks in E_2s_4 have high quality and great potential for hydrocarbon generation and expulsion. E_2s_4-derived oils migrated for a short distance and dispersedly accumulated in the deep or buried-hill traps near the kitchen,but only a few of them have been found. Such a petroleum distribution pattern has important implications for future exploration. There is considerable exploration potential for E_2s_4-derived oils in the deep traps and buried-hill traps in the Baxian Sag.